HTTP Error 503: Service unavailable when testing Realtime Service on Dynamic AX 2012 R3

HTTP Error 503: Service unavailable when testing CDX Realtime Service on Dynamic AX 2012 R3 CU8

The syntax above raise when test CDX Realtime Service on IIS

The Solution is :

Try check your account name for running service CDX Realtime  (Length of account shouldn't exceeds (20)

example :  DevRealTimeServiceAcc (21) 

thil will cause an error when we browse Realtime Service In IIS with the account by example, because the system only read (20 char) whic is DevRealTimeServiceAc